1. Field of the Invention
The invention relates to a direct current-electric arc furnace system comprising a furnace vessel, one or more electric arc electrodes, connected as a cathode, a bottom contact connected as the anode, a furnace transformer and a rectifier assembly for feeding the furnace, and an electrode control system and a current regulator, whereby a choke is switched into the direct-current lines from the rectifier to the bottom contact.
The starting point for the invention is an electrode control, which is, for example, the subject matter of the European patent application 0 498 239.
2. Description of the Related Art
In direct current-electric arc furnace systems the electric arc jumps suddenly in the course of the melt-down process from one piece of scrap to the other. In this manner the length and resistance of the electric arc changes suddenly. A dynamic, high quality current regulator has the task of limiting the resulting current changes to a minimum, in order to protect the rectifier of the controller even in extreme cases, e.g. when the electrode short-circuits with the scrap, from overloads and eventual distruction of the thyristor converters.
Both the current fluctuations and to a greater degree the widely varying modulation phase angle of the rectifier produce, due to the control action, reactive load surges at the supply network.
These reactive load variations are critical for the fluctuations in voltage at the supply network. If they exceed a certain limit, the consumers connected to the same network are disturbed. The fluctuations in voltage can be perceived in an unpleasant manner by means of light fluctuations, socalled flicker.
Official specifications force the operators of such systems to measures that virtually eliminate the flicker. If an expansion of the supply mains is out of the question, the only possibility to date has been to equip the furnace system with a SVC device (SVC =Static Var Compensation--static flicker compensation). Cf. the corporate document of BBC Brown Boveri AG, Baden (Switzerland) "Electric Arc Systems `Arcmelt`, AL model series", document no. CH-IH 512 484, undated, where on pages 20-22 a reactive power and flicker compensation for three phase electric arc furnace systems is described and shown, or U.S. Pat. No. 5,155,740, whose subject matter is a flicker compensator for direct current electric arc furnace systems. However, such devices for direct current-electric arc furnace systems are expensive, since they require high power rectifiers, chokes and capacitors.